1. Field of the Invention
The invention pertains to a torsional vibration damper for a hydrodynamic torque converter, the damper having an input section including a converter cover and an output section including a hub disk which is non-rotatably connected to a hub which can be centered on a transmission shaft. A bridge clutch includes a piston connected to said hub disk via stored energy elements which permit relative movement. The piston can be brought into working connection with the converter cover by means of at least one friction surface.
2. Description of the Related Art
U.S. Pat. No. 6,273,226 discloses torsional vibration damper for a hydrodynamic torque converter which works together with a bridge clutch equipped with a piston. Cover plates, which act as the input section of the torsional vibration damper, are attached to the piston of this bridge clutch, and each of these plates has circumferential openings, which hold stored-energy elements. These devices can be operated by actuating areas on the cover plates. The stored-energy elements are supported at the other end by a hub disk, the radially outer area of which is provided with radial projections. The hub disk serves as the output section of the torsional vibration damper. The radial projections project into the axial area between the two cover plates and include actuating areas for the stored-energy elements.
The radially inner end of the hub disk, according to FIG. 1 of the patent, is nonrotatably connected by gear teeth to a hub, which also has a radially outward-projecting hub flange, so that it can be connected to the base of the turbine wheel of the hydrodynamic torque converter, this connection being accomplished by means of rivets. On the transmission side, the hub is braced by an axial support on the hub of the stator of the hydrodynamic torque converter. The other end of the stator is supported by another axial support on a converter hub on the transmission side.
The previously mentioned hub is referred to in technical circles as a xe2x80x9cturbine hubxe2x80x9d, which, because of its complicated geometric design with areas of different thickness, can be produced as a forging, as a casting, or as a sintered part. Because these types of production methods do not lead to surface qualities or dimensional accuracies which are sufficient to meet the requirements imposed on turbine hubs, it is usually necessary to subject the workpieces to a machining process such as turning to achieve the required surface quality and the desired narrow tolerances. If the turbine hub is produced by a casting operation, problems involving strength and the porosity of the surface must also be dealt with, whereas production by means of a sintering process makes it necessary to accept higher production costs and welding problems, again because of high porosity.
Another disadvantage of the design of the hydrodynamic torque converter described in FIG. 1 of the above-cited patent is the expense associated with the use of rivets to connect the turbine base to the radial flange of the turbine hub, because measures must be taken to ensure proper centering, and openings must be provided for the rivets. In addition, the axial support which braces the turbine hub in the direction toward the stator is not centered and thus lacks accurate guidance. It should also be pointed out that, when the piston of the bridge clutch executes movements in the axial direction, the entire torsional vibration damper must be moved along with it, which increases both inertia and wear. The torsional vibration damper is therefore connected to the turbine hub by means of a set of gear teeth, so that it can perform this type of axial movement.
Although the last-mentioned problem is not present when the hub disk of the torsional vibration damper is connected to the turbine hub by peening as shown in FIG. 6, it can nevertheless be seen in conjunction with FIG. 7 that this advantage is purchased at the cost of even greater production and joining work.
The invention is based on the task of designing a torsional vibration damper for a hydrodynamic torque converter in such a way that, first, both high strength and dimensional accuracy are obtained at the least possible production cost and, second, that these advantages can be obtained with the use of a minimum amount of material.
According to the invention, the hub disk extends radially inward to the outside circumference of the hub, where it is attached directly to the hub.
Because the hub disk is extended radially inward to the area of the outside circumference of the hub and is attached directly to the hub at that point, it is possible to do without a xe2x80x9cturbine hubxe2x80x9d entirely. Instead, a hub of very simple design can be used, which, if desired, can be completely free of radial projections; and because the hub disk of the torsional vibration damper extends directly up to the hub, it is even possible to omit a hub flange as well. As a result of this constructive design, the hub, as far as its function is concerned, becomes a xe2x80x9ctorsional vibration damper hubxe2x80x9d and thus offers the best possible design for a torsional vibration damper with an output part which is to be brought directly into rotational connection with the transmission output shaft. A torsional vibration damper of this type is referred to in technical circles as a xe2x80x9cturbine damperxe2x80x9d.
Aside from the previously mentioned functional advantage of the object according to the invention, there are also special advantages to be obtained with respect to production technology, which are reflected in very favorable production costs. Thus the hub disk can be produced from standard commercial sheets or plates by simple stamping, possibly combined with a light drawing operation; the stamping operation can be performed with such precision that no problems with dimensional accuracy are encountered. The choice of sheets or plates obviously also ensures that the hub disk will have the required smooth surface and will be easy to weld. This latter feature is especially important, because it means that the hub disk can be permanently connected to the other components in a technically simple, precise, and low-cost manner. Thus the performance of a welding operation to join the hub disk to the hub is advantageous, and, of course, the hub itself should also be made of a material which allows optimal welding. It is easy to make an appropriate choice of material for the hub, because it is of very simple design and can thus be produced by cold forming, preferably by cold pressing. This pressing operation can be accomplished in a single pass through a line of presses or possibly even on a single press. It is well known that, when cold forming of this type is used, the dimensional accuracy and the surface condition are of such high quality that no subsequent machining operations are required.
It is also advantageous to attach the base of the turbine wheel of the hydrodynamic torque converter to the hub disk by welding. As a result, it is possible to omit entirely the turbine hub normally used in hydrodynamic torque converters. Thus, thanks to the way in which the hub disk according to the invention is designed and to the way in which it is connected both to the hub and to the turbine base, an overall configuration is achieved which is characterized by the minimal use of material. In addition to the advantages previously described, the overall power takeoff side of the hydrodynamic torque converter also has an especially light-weight and thus low-inertia design.
In regard to the previously mentioned welds between the hub disk and the hub and between the hub disk and the turbine base, it should be pointed out that all of the knowledge concerning welding on hydrodynamic torque converters such as that conveyed in DE 197 55 168, should be applied here. In particular, the laser welding method can be considered especially advantageous for making the present connections.
Because the hub is designed with an axial contact surface for the hub disk, furthermore, the hub disk is fixed axially in position with respect to the hub in addition to being centered radially, as already provided in any case, so that, especially when this axial contact surface is produced by a section of increased radial dimension on the outside circumference of the hub, this radially enlarged section serves as an axial contact surface for the hub disk, so that, when the weld is made from the opposite side, it is possible to produce an absolutely rigid connection between the hub disk and the hub. Fastened axially in this way to the hub, the hub disk can then be used to limit the axial movement of the piston of the bridge clutch toward the transmission side, which piston can be mounted with freedom of axial movement on a section of the outside circumference of the hub. To this extent the hub disk serves as an axial contact surface for the piston in this direction of motion. In the opposite direction, the piston comes to a stop when a friction lining attached to it or a friction surface provided on it makes contact with an opposing friction surface of any suitable type, which, in turn, is supported axially against the converter cover on the internal combustion engine side. To give the piston this freedom of axial movement without as a result being forced to move the entire torsional vibration damper, including the turbine wheel, it is provided that the cover plates, attached to the piston to serve as the input parts of the torsional vibration damper, are arranged at predetermined axial distances from the hub disk. This axial distance is preferably calculated in such a way that the piston can reach its limit position on the converter cover side or on the hub disk side before the cover plate assigned to this direction of movement is able to make axial contact with the corresponding side of the hub disk and thus hinder or even to prevent such movement.
Because the piston, as already described, has an axial stop on the hub disk, the hub disk must also have support of its own in the direction toward the transmission side, for which reason an axial support is provided on this side, next to the hub disk. Because an axial support of this type should logically be centered, so that it will not cause wear as a result of radial movements during operation, whereas at the same time the hub disk should have an essentially uniform material cross section in its radial dimension, a result which is obtained by the use of flat-surfaced sheets or plates as a starting material, the axial support is centered at a different point, namely, at the hub of the stator of the hydrodynamic torque converter. The side of this stator hub facing away from the hub disk is braced by another axial support against the converter hub on the transmission side. Radially, however, the stator hub is mounted on a hollow support shaft by way of a free-wheel device in the conventional manner, where, with respect to the engineering design of a support shaft of this type, U.S. Pat. No. 5,575,363 discloses ways in which the stator can be held in place radially and ways in which the flow paths for the control of the piston of the bridge clutch can be laid out.
Let us return to the base of the turbine wheel, which is attached by a welding operation to the hub disk. It should be noted that, as a result of the introduction of bent sections, this base shows a high degree of elasticity in the axial direction. Axial vibrations which have been transmitted from the crankshaft via the piston of the bridge clutch, the hub, and the hub disk to the turbine base can thus be effectively reduced before they are transmitted onward to the turbine wheel.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.